Currently known processes for the production of formaldehyde by oxidation of methanol on a catalytic bed formed by two or more layers having different catalytic activity use the layer of lower activity, formed by mixtures of pure catalyst with inert material which is by far more diluted and longer than in previous processes in order to have relatively low maximum hot spot temperatures in this layer, generally comprised between 330° C. and 350° C. These temperatures, after a short period of activity of the layer, tend to decrease and in the final steps become lower than in the layer formed by pure catalyst.
By working under such conditions, the life of the catalyst decreases significantly. The decrease requires frequent reloading of the catalyst in the tubes of the tube bundle, an operation which is long and expensive and causes frequent stops of the plant. Moreover, there is the need to recover the molybdenum from the spent catalyst, imposed by the high price currently reached by this metal.